In the coming year we intend to characterize the iodopeptides obtained via the N-carboxy anhydride polymerization method. Emphasis will be placed on analyzing the monomer ratios in the final product, molecular weight distributions, and the degree of iodination. The action mechanism of iodopeptides will be studied by examining the question whether they are direct inhibitors of thrombin. This will be approached by measuring the effect of the iodopeptide on thrombin when acting as an esterase on a synthetic substrate TAME (Tosylarginine methylester). Experiments will also be conducted to measure the effect of the presence of iodopeptides on the appearance of fibrinopeptides in the coagulation of plasma. These experiments could decide whether iodopeptides inhibit thrombin directly, the fibrin monomer- polymerization step, or both. Further developmental work will be carried out on polycysteic acid, focusing on its optimum preparation, and substitution of cysteic acid for glutamic acid as a monomer in iodopeptides. Coagulation and toxicity studies will be included. Finally, we plan to continue our current effort in the study of the mechanism causing prolonged bleeding times by iodopeptides. Both in vivo and in vitro studies are planned, the latter by platelet aggregation and adhesion.